The present invention relates to a method for the production of a trim part for decorative purposes and to a trim part produced by the process.
German Published Patent Application No. 296 04 026 describes a utility article having a substantially two-dimensional form and a facing or masking layer made from a brittle natural material, especially stone or a stonelike substance, which is fragile in thin layer form. The facing or masking layer is disposed on a support layer made from a fiber-reinforced material with a plastic matrix. The utility article can however be employed only to a limited extent as a trim part for decorative purposes because its substantially two-dimensional form makes it impossible to use for trim parts with three-dimensional curvature of their surfaces.
German Published Patent Application No. 297 12 329 describes a three-dimensionally curved molding made from a laminated material, in which the decorative elements consist of fibers or a fiber mat. The shape of the three-dimensionally curved part is determined by a molding produced by deep drawing. In this method, however, the use of a brittle material that is fragile in thin-layer form is impossible.
German Published Patent Application No. 39 30 603 describes a trim part and a method for its production, the trim part having a surface shape with a three-dimensional curvature. The final shape is determined by two workpiece molds serving to provide the shape, an upper mold and a lower mold, being laid and hardened in these molds. Thus, only flexible materials can be used as decorative inserts. The use of a brittle material that is fragile in thin-layer form, such as, for example, natural stone, is impossible because of the bending of the material of the decorative insert necessary for shaping purposes.
In a conventional trim part for decorative purposes, especially for interior use, and preferably for the interior trim of passenger compartments of motor vehicles, a decorative layer of a natural material, especially natural stone, is applied on the visible side of a base part. The decorative layer of natural stone can in this method be produced in any desired three-dimensional form. To achieve this, large quantities of the natural substance are used, the desired final surface shape being produced by milling from a solid material. The milled layer is retained on a supporting element, on which it remains in subsequent use. The method allows substantial freedom of design, but suffers from the serious disadvantage of long processing times and a high material input.
It is therefore an object of the present invention to provide a method for the production of a trim part for decorative purposes, especially for the forming of interior and/or exterior trim parts for motor vehicles, having an ornamental layer made from an inorganic and/or crystalline material that is fragile in thin-layer form, wherein the material input for the ornamental layer is minimized and the optical properties of the ornamental layer are at least approximately preserved.
It is a further object of the invention to provide a trim part for decorative purposes with an ornamental layer in which an at least approximately free geometrical and optical design of the trim part is possible.
The above and other beneficial objects of the present invention are achieved by providing a method as described herein.
The method according to the present invention provides the advantage that a maximum optical effect may be achieved with a low material input of the material for the ornamental layer. The ornamental layer may be brought by the upper and lower molds of the casting mold into the three-dimensional form determined by the particular casting mold. The thin ornamental layer, applied to a flexible stabilizing material, may be shaped as desired in three dimensions by the closing upper and/or lower mold. The ornamental layer is fixed in its predetermined form by the protective layer. As a result there are many possible geometrical designs for the trim part.
The brittle material of the thin ornamental layer according to the present invention, which is fragile in thin-layer form, may fracture along microstructures or crystal edges, but the overall optical impression is not critically changed thereby. The microfine fractures, for example, along crystal boundaries in the case of crystalline materials, are concealed by the protective layer, so that no irregularities are apparent on the surface of the trim part, and, as a result of the fact that the crystals or inorganic microstructures themselves are not destroyed, the optical properties of the inorganic and/or crystalline material of the thin ornamental layer are substantially perfectly preserved.
The flexible stabilizing material may hold the ornamental layer together even when the latter would otherwise collapse because of the fractures described above. A further advantage of the stabilizing material is that it stabilizes the ornamental layer and substantially facilitates handling and transportation of the thin ornamental layer.
As a result of the transparent or partially transparent configuration of the covering layer and the supporting element, it is possible, by backlighting the ornamental layer (by introducing light, for example, by a lighting wire or with two-dimensional lighting devices such as electroluminescent foil) to achieve further optical effects as a result of the light passing through the material used for the ornamental layer, for example, natural stone.
The surface of the casting mold facing what will subsequently be the visible side of the trim part may be designed with very fine surface roughness, so that the transparent or at least partially transparent plastic curing at this surface has a very smooth and uniform surface, making it possible to eliminate further processing of the visible side of the trim part.